1. Field of the Invention
The present invention is directed to iridium (III) complexes used as emissive materials in electroluminescent (EL) devices, and in particular organic light emitting devices (OLEDs).
2. Description of the Related Art
OLEDs are typically comprised of at least a layer of emissive material sandwiched between an anode, typically comprised of a transparent conductor such as indium-tin oxide, and a cathode, typically a low work-function metal, such as magnesium, calcium, aluminum, or the alloys thereof, with other metals. When a bias is applied across the electrodes, positive charges (holes) and negative charges (electrons) are respectively injected from the anode and cathode into the emissive layer. The holes and the electrons form excitons in the emissive layer to emit light.
Many metal-ligand complexes have been used in the emissive layers of OLEDs, including blue light emitting layers made from trivalent metal quinolate complexes, Schiff base divalent metal complexes, metal acetylacetonate complexes, metal bidentate ligand complexes, and rare earth mixed chelates, as well as red light emitting layers made from luminescent iridium (I), rhodium (I), and platinum (II) dithiolate complexes. These metal-complexes can be used in conjunction with organic dyes.
The synthesis of a luminescent tris(2,2′-bipyridine)iridium(III) ion is disclosed in Journal of the American Chemical Society, Vol. 96, No. 6, 1959–60 (1974).
International Application WO 01/41512 discloses metal complexes suitable for use in OLEDs, having a metal species associated with three bidentate ligands. The metal species is coordinated with an sp2 hybridized carbon and a heteroatom of the ligands.